Multiple stage polymerization processes are known in the art as is the use of metallocene catalyst systems. Multiple stage polymerization processes, such as two-stage polymerization processes, are generally used to prepare block copolymers which contain rubbery materials. Two-stage polymerization process products may include propylene block copolymers. In some instances, the propylene/ethylene copolymer portion of these block copolymers may be rubbery. In these instances, these products may be more suitable for molding applications rather than films. In other instances, two or more metallocenes may be used for the preparation of isotactic propylene polymers.
Related patents and patent applications include: U.S. Pat. Nos. 5,280,074, 5,322,902, 5,346,925, 5,350,817, 5,483,002 and Canadian Patent Application No. 2,133,181.